For pastry: mix dry ingredients, pinch in butter. Add egg yolks and work until dough holds together and is homogeneous and soft. Roll ⅛” thick, cut bottom of tart and fit strips to the side. Chill at least 1 hour. If using perforated tart ring, you can bake without weights. Bake 350 degrees until golden brown. Cool.
For filling: whisk water, sugar, salt, and cream of tartar in saucepan. Whisk over medium heat until just boiling. Add butter. Whisk until just boiling. Add ⅓ of hot mixture into whisked egg yolks, then return to pan and whisk until combined thoroughly. Whisk in calamansi juice. Whisk over medium heat until it starts to boil, then continue whisking for 1 minute. Remove from heat and turn in to prepared crust. Cool at room temperature for at least 90 minutes.
Set bowl of stand mixer over simmering water. Add whites, sugar, and cream of tartar and whisk until exactly 165 degrees. Remove bowl from heat and fit to stand mixer. Whisk until meringue peaks form and bowl is no longer warm to the touch.
Spoon meringue over filled crust and torch.